Isotactic polypropylene (iPP) was crystallized using temperature modulation in a differential scanning calorimeter (DSC) to thicken the crystals formed on cooling from the melt. A cool-heat modulation method was adopted for the preparation of the samples under a series of conditions. The effect of modulation parameters, such as temperature amplitude and period was monitored with the heating rate that followed. Thickening of the lamellae as a result of the crystallization treatment enabled by the cool-heat method lead to an increase in the peak melting temperature and the final traces of melting. For instance, iPP melting peak shifted by up to 3.5°C with temperature amplitude of 1.0°C while the crystallinity was increased from 0.45 (linearly cooled) to 0.53. Multiple melting endotherms were also observed in some cases, but this was sensitive to the temperature changes experienced on cooling. Even with a slower underlying cooling rate and small temperature amplitudes, some recrystallization and reorganization occurred during the subsequent heating scan. The crystallinity was increased significantly and this was attributed to the crystal perfection that occurred at the crystal growth surface. In addition, temperature modulated differential scanning calorimetry (TMDSC) has been used to study the melting of iPP for various crystallization treatments. The reversing and non-reversing contribution under the experimental time scale was modified by the relative crystal stability formed during crystallization. Much of the melting of iPP was found to be irreversible.
Inorganíc polymers such as silicates, borates and phosphates can be transformed into amorphous solids by heating to an appropriate
temperature. Thermal amorphization can be obtained by: 1. thermal dissociation of a crystalline compound, 2. distortion of
the crystal structure of a solid during prolonged heat treatment, without change of its chemical composition. The specificity
of the materials received, the crystallochemical conditions necessary for the amorphization which takes place, and the high-temperature
processes of internal structure reconstitution and recrystallization in the amorphous products are considered.
Authors:F. Rey, O. Chamorro, F. Martín Gil, and J. Martín Gil
The thermal stability of selected straight-chain (C6-C14) esters of fatty acids has been studied by TG-DTG and DTA analysis. In DTG, a peak is detected between 84° and 125° C followed
by a main effect in the range 105°–215°C, whereas in DTA only an exothermic peak appears in the range of 126.5° to 187°C (onset
temperatures). The temperatures of these effects have been related with ignition points, molecular weights and boiling points.
The characteristics of melting and recrystallization of the above fatty acid methyl esters and those with carbon numbers between
C14 and C24 have been established by DSC along the melting range between −83° and 50°C. Polymorphism appears in caproic, heptanoic, palmitic
and stearic acid methyl esters.
We studied thermal transitions and physical stability
of oil-in-water emulsions containing different milk fat compositions, arising
from anhydrous milk fat alone (AMF) or in mixture (2:1 mass ratio) with a
high melting temperature (AMF–HMT) or a low melting temperature (AMF–LMT)
fraction. Changes in thermal transitions in bulk fat and emulsion samples
were monitored by differential scanning calorimetry (DSC) under controlled
cooling and reheating cycles performed between 50 and –45C (5C
min–1). Comparison between bulk fat samples
and emulsions indicated similar values of melting completion temperature,
whereas initial temperature of fat crystallization (Tonset)
seemed to be differently affected by storage temperature depending on triacylglycerols
(TAG) composition. After storage at 4C, Tonset
values were very similar for emulsified and non-emulsified AMF–HMT blend,
whereas they were lower (by approx. 6C) for emulsions containing AMF
or mixture of AMF–LMT fraction. After storage at –30C, Tonset values of re-crystallization
were higher in emulsion samples than in bulk fat blends, whatever the TAG
fat composition. Light scattering measurements and fluorescence microscopic
observations indicated differences in fat droplet aggregation-coalescence
under freeze-thaw procedure, depending on emulsion fat composition. It appeared
that under quiescent freezing, emulsion containing AMF–LMT fraction
was much less resistant to fat droplet aggregation-coalescence than emulsions
containing AMF or AMF–HMT fraction. Our results indicated the role of
fat droplet liquid-solid content on emulsion stability.
In mineralogical research differential thermal analysis can be applied as either a single or a combined method for three purposes:1.for the qualitative identification of minerals and the (semi-)quantitative determination of the components of rocks and soils,2.for the characterization of crystal-physical and crystal-chemical properties, including the study of kinetics and the determination of thermodynamic data, phase and reaction equilibria,3.for special petrogenetic investigations concerning the interrelation of mineralogical properties with the formation, decomposition or recrystallization of minerals.
Authors:Szabolcs Nagy, Sándor Józsa, Arnold Gucsik, Szaniszló Bérczi, Kiyotaka Ninagawa, Hirotsugu Nishido, Miklós Veres, Ákos Kereszturi, and Henrik Hargitai
We studied optical microscopic and micro-Raman spectroscopic signatures of shocked olivine from the ALH 77005 Martian meteorite sample. The purpose of this study is to document pressure and temperature-related effects in olivine over the entire sample, which can aid in understanding structural changes due to shock metamorphism and the post-shock thermal annealing processes of lherzolitic Martian meteorites. According to the optical microscope observations, three areas may be discernible in olivine of the ALH 77005 in the vicinity of the melt pocket. The first area is the thermally undisturbed part of a grain, which contains a high density of shock-induced planar microdeformations such as Planar Deformation Features (PDFs) and Planar Fractures (PFs). Compared to the first area, the second area shows less shock-induced microstructures, while the third area is a strongly recrystallized region, but not formed from a melt.
A common Raman spectral feature of these olivines is a regular doublet peak centered at 823 and 852 cm−1; additionally, two new peaks at 535 and 755 cm−1 appear in the weakly annealed transition zones.
This paper is devoted to the description of spessartine-almandine garnet (Sps: 39.8-60.2%; Alm: 29.1-56.76%; Grs <7%, Prp <3.6%, Adr <5%) from aplitic dyke rocks of the Mórágy granitoid near Erdõsmecske and Aranyos valley. The aplitic dyke rocks contain K-feldspar, plagioclase, quartz, (myrmekite), ±garnet, ±biotite, chlorite or secondary muscovite, ±ore minerals, ±calcite, ±apatite and ±epidote. Two different zoning types in garnet were detected by electron microprobe. Zoning type I means either Mn enrichment at the expense of Fe towards the rim or towards the core or plateau garnet profiles. Zoning type II displays Ca enrichment at the rim of garnet. A high proportion of Sps component in garnet and the character of zoning type I are considered as typical magmatic features. The pressure-temperature estimation for aplite formation arises from experimental investigations of Green (1977) in agreement with the hypothetical approach of liquidus relationships by Abott and Clarke (1979) giving a minimum temperature estimation of c. 675 °C-700 °C at pressure of 1-3 kbar. Following the magmatic crystallization, solid state deformation is evidenced by dynamic recrystallization of quartz and feldspars at temperatures of about 450-500 °C in the upper greenschist to lower amphibolite facies. Grossular-rich rim of garnet indicates pressure increase during ductile deformation.
Authors:Nathaniel B. Zuckerman, Maxim Shusteff, Philip F. Pagoria, and Alexander E. Gash
The secondary high explosive 2,6-diamino-3,5-dinitropyrazine-1-oxide, or LLM-105, has been synthesized using a commercially available flow microreactor system. Investigations focused on optimizing flow nitration conditions of the cost effective 2,6-diaminopyrazine-1-oxide (DAPO) in order to test the feasibility and viability of flow nitration as a means for the continuous synthesis of LLM-105. The typical benefits of microreactor flow synthesis including safety, tight temperature control, decreased reaction time, and improved product purity all appear to be highly relevant in the synthesis of LLM-105. However, the process does not provide any gains in yield, as the typical 50—60% yields are equivalent to the batch process. A key factor in producing pure LLM-105 lies in the ability to eliminate any acid inclusions in the final crystalline material through both a controlled quench and recrystallization. The optimized flow nitration conditions, multigram scale-up results, analyses of sample purity, and quenching conditions for purity and crystal morphology are reported.
Authors:M. Z. El Sabee, W. G. Perkins, R. S. Porter, V. G. Baranov, and S. Ya. Frenkel
The thermal and mechanical behaviour was measured in the U. S.for a polyethylene that had been prepared and highly drawn in the U. S. S. R. The melting point and percent crystallinity were evaluated in this studies as a function of heating rate and recrystallization. The Young's modulus and tensile stress to break in the orientation direction were 4.1 and 0.15 GPa, respectively.The tensile strain to break was about 8%.
Authors:A. Raemy, C. Kaabi, E. Ernst, and G. Vuataz
The DSC curve of freeze-dried amorphous sucrose shows the glass transition, the crystallization and the melting (just before
decomposition) of the sample. Sucrose crystallization occurs below 100°C: this phenomenon can therefore be observed with the
microcalorimeter Setaram Micro-DSC used in the scanning mode. Mixtures of amorphous and crystalline sucrose in known proportions
were used to calibrate the instrument. Low level amorphism (down to about 0.5%) could be detected and quantitatively evaluated
on the basis of the crystallization enthalpies determined. The calibration curve obtained can be applied to determine the
degree of amorphism in milled sucrose. A simple gravimetric method, based on the desorption of water induced by recrystallization
of the amorphous layer can be used to obtain similar data more rapidly. This simple method is particularly useful for controlling
the amorphism on line during a process, and is also briefly described.